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expected_data.txt
XML via UDP - expected data from hosts ====================================== <<< Provisional, pjm2@kent.ac.uk >>> Purpose of this document ------------------------ This document shall help to provide a separate party with the knowledge required to use their own implementation of a piece of host monitoring software. In particular, this document details the data that is to be expected from a host. This document is additional to http://www.i-scream.org/cgi-bin/docs.cgi?doc=specification/xml_via_udp.txt Background ---------- Hosts are expected to periodically send UDP packets to the central monitoring system. Such packets may contain various pieces of information about the host, such as how much free memory is remaining on the host, etc. Some of this data is deemed to be 'essential', some is 'expected' and the rest is not necessary, but shall not be ignored by the central monitoring system server. Specification ------------- The UDP packet must contain a complete and well-formed piece of XML markup, describing the data that the host is submitting. In the event of a piece of data containing an invalid character, such as a "<", it is the responsibilty of the host to format this in a valid manner, for example by replacing all occurrences of "<" with "<" before it is sent in a UDP packet to the central monitoring system server. Alternatively, the data may be wrapped up in special CDATA tags. For example, if we wish to send the following text: <>&!" surrounded by <test_chars> tags then we can safely send this by wrapping it up to produce the following XML snippet: <test_chars><![CDATA[<>&!"]]></test_chars> The bare minimum that a host should send is the following: - <packet> </packet> Note that every XML tag must also have a matching closing tag. However, such a packet is rather useless when it is received by the server - it does not provide any useful information. As such, a packet will be rejected by the server if it does not specify the machine_name, its I.P. address (ip), a packet sequence number (seq_no) and a date. Note that the date is a long integer representing the number of seconds since the epoch. All of these are expected to be specified as an attribute of the packet tag. If they are not specified here, then the packet will be rejected. Thus, to ensure that a packet has a chance of being acted upon, a host must specify at least four attribute values - machine_name, ip, date and seq_no. These must be formed in the style shown below. <packet machine_name="raptor" ip="aaa.bbb.ccc.ddd" date="93456245245" seq_no="1234567"> </packet> Note that the server may run additional 'plugin' tools that are designed to filter/reject packets under certain conditions. Please check with the server administrator if you wish to know about the specific configuration of your central monitoring system. The I.P. address and machine_name could be found from the UDP packet itself, but these remain essential so as to provide resiliance from stray packets that do not contain any valid or useful data. Remember that malformed XML data would be rejected by the central monitoring system immediately, without acting upon it. Classification of XML data in our system ---------------------------------------- ESSENTIAL: - The following values are ESSENTIAL in each packet. Any packet without these will be rejected. They MUST be specified as attributes of the root node ("packet"): - ip seq_no date machine_name EXPECTED: - The following values are EXPECTED in each packet. All packets are RECOMMENDED to specify these values, as the server is designed to permanently store such data in an easy and quick to access manner. It is not essential to specify such values, but it does limit the usefulness of the central monitoring system if these values are not specified: - mac_address (attribute) os_name (attribute) os_version (attribute) cpus * load * memory * swap * disk * users (attribute) * - These parameters are specified with tags of the same name. They contain nested XML tags. See later in this document for more details about that! All of the values marked as being attributes above must be specified as an attribute of the root tag ("packet") OTHER: - Any other arbitrary values may be specified by the host. The only provision here is that they may not share the same name as another tag or attribute within the same heirarchical level. The server will be able to handle such clashes, however, it cannot be guaranteed which of the duplicate parameters would gain priority. Detail of a complete 'expected' XML packet via UDP -------------------------------------------------- I shall start by showing an example of a complete 'expected' packet. I shall then explain the contents of it. Here is an example of an XML packet, containing all of the 'essential' and 'expected' data: - <packet ip="" seq_no="" date="" machine_name="" mac_address="" os_name="" os_version="" user=""> <cpus> <cpu0></cpu0> <cpu1></cpu1> <cpu2></cpu2> </cpus> <load> <load1><load1> <load5><load5> <load15><load15> </load> <memory> <free></free> <total></total> </memory> <swap> <free></free> <total></total> </swap> <disk> <p0> <free></free> <total></total> <mounted></mounted> <label></label> </p0> <p1> <free></free> <total></total> <mount></mount> <label></label> </p1> </disk> </packet> Note that linefeeds and spaces would normally not be present. These are only shown above for structure clarity. Note that all of the essential attributes have been specified as attributes of the root node. The expected attribute values are also attributes of the root node. The <cpus> tag begins a list of cpu load information. Each subtag herein must be of the form cpux, where x is the number of the processor in multiprocessor systems. Note that this numbering starts from zero. The <load> tag begins a list of system load information. The load tag is only expected to contain 3 subtags, named "load1", "load5" and "load15". These represent the average load 1 minute ago, 5 minutes ago and 15 minutes ago respectively. The <memory> tag begins a list of system memory information. This tag is only expected to contain two subtags, as shown in the example above. These two subtags specify how much memory the system has free and how much memory the system has in total. The <swap> tag is identical in nature to the <memory> tag. The <disk> tag begins a list of partition information. Each subtag must be of the form px, where x is the number of the disk partition that is unique for that particular system. Note that the numbering of px is expected to start from zero. Each <px> tag contains the following subtags: - <free> - the free partition space in bytes. <total> - the total partition size in bytes. <mount> - the mount point, eg, "/var". <label> - the label of the physical disk. The <disk_total> tag begins a list of total disk space, similar in implementation to the <disk_free> tag. Any other values and attributes may be specified in the packet, providing they are not specified in the same heirarchical level as another attribute or value with the same name. Flexibility and Minimising bandwidth ------------------------------------ The following issues still stand: - The means of submitting host data via UDP containing XML markup is provided so that future customisation is easily possible. It would be possible to easily tailor a custom piece of host monitoring software to provide exactly what data is desired for adequate monitoring. Some of the XML markup demonstrated above contains a lot of rendundant features. For example, it is not necessary to lay the contents out neatly (although this certainly helps visualise the contents). The amount of data sent within each UDP packet may be (in some cases, vastly) reduced by using some of the ideas described below: - - Remove unnecessary linefeeds and 'white space' - If a single piece of data is to be represented, it will usually occupy less space if it is stored as an attribute to a tag, rather than within a pair of tags. - Comments within the XML may be useful for testing purposes, however, the server ignores all comments so these can be removed to reduce packet sizes. Taking the above into account, here is an example of some ideally formed XML to be contained within a UDP packet: - <packet machine_name="raptor" ip="aaa.bbb.ccc.ddd" ><freespace><drive1>23677</drive1><drive2>23534</d rive2><drive3>10390</drive3></freespace></packet> Notice how all unnecessary 'white space' and linefeeds have been removed. The comment has also been removed. Values such as "machine_name" and "ip" have both been stored as an attribute of the root node ("packet") as this results in a smaller packet size. About ----- This document was written by Paul Mutton [pjm2@kent.ac.uk] for use by the team working on a 3rd year Computer Science project called "i-scream". More details can be found on the project website - http://www.i-scream.org
